CODEWITHSUNDEEP
python
SohrabFarjami
SohrabFarjami

Reputation: 19

How to return next line in text file in python

def openFood():
    with open("FoodList.txt")  as f:
                lines = f.readlines()
                for line in lines:
                    if 'Food' in line:
                        print(f.next())
openFood()

I want it where when it sees a certain header like 'Food' It will print the line below it. I cant seem to make it work. The text file will be like

Food
Apple
Cal 120
Protein 12
Fat 13 
Carb 23

Upvotes: 2

Views: 417

Answers (6)

Standard_101
Standard_101

Reputation: 325

readlines() reads all the lines in a file and returns a list. You could either read and iterate one line at a time (using readline()), or read all the lines and use the list for iteration (using readlines()).

Apart from the ways mentioned, you could also use a bool like below (I've used readlines() here):

def openFood():
    with open("FoodList.txt")  as f:
        lines = f.readlines()
        trigger = "Food"
        triggerfound = False

        for line in lines:
            if triggerfound:
                print(line)
                triggerfound = False

            if trigger in line:
                triggerfound = True

openFood()

Upvotes: 0

Cow
Cow

Reputation: 3030

Reading a file one line at a time can be beneficial if the file is very large. This code will not load the full file into memory, but only one line at a time:

def openFood():
    with open("FoodList.txt") as f:
        line = f.readline()
        while line:
            if 'Food' in line:
                print(f.readline())
            line = f.readline()

openFood()

Result:

Apple

Note: This method will be a lot slower for smaller files, than reading the contents into memory using the readlines() method.

Upvotes: 0

funnydman
funnydman

Reputation: 11346

Method readlines() returns list object, you can convert it to an iterator and then use next function:

def openFood():
    with open("FoodList.txt") as f:
        lines = iter(f.readlines())
        for line in lines:
            if 'Food' in line:
                print(next(lines))
openFood()

Upvotes: 0

Schnitte
Schnitte

Reputation: 1217

Since readlines() returns a list of the lines in the file that you can iterate over, you can simply access the subsequent line via its index:

l = len(lines)-1
for i in range(l):
    if 'Food' in lines[i]:
        print(lines[i+1])

Upvotes: 0

Jeril
Jeril

Reputation: 8521

Can you try the following:

def openFood():
    with open("FoodList.txt")  as f:
        lines = f.readlines()
    for ind, line in enumerate(lines):
        if 'Food' in line:
            try:
                print(lines[ind + 1])
            except:
                print('No line after "Food"')
openFood()

Upvotes: 0

Rodrigo Llanes
Rodrigo Llanes

Reputation: 640

Just use the index.

def openFood():
    with open("FoodList.txt")  as f:
        lines = f.readlines()
        for i in range(len(lines)-1):
            if 'Food' in lines[i]:
                print(lines[i+1])
openFood()

Upvotes: 2

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